Originally Posted by
Houba
Voting is not always the best solution. Try to block 2 pitots tubes on 2 ADMs at FL290 (at night) on the Triple and perform a descend for landing and land.
I am new to pprune forgive me I dont know how to simply add a comment so I've hit reply to yours, here's my pound or kilo of flesh:-
Basically the MCAS trim override system is a partial “FbW” system. We all know why it was implemented, so I don’t need to discuss its merits/functionality here or the unsettling fact that its bad behaviour was actually notified last year after the Lion Air incident. No one outside of Boeing or whoever is in accident investigations has seen the recorder data sets and heard the recently recovered CVR of that accident. That will remain confidential for ever.
I personally doubt (working in military electronics) whether the latest incident’s recorders would have survived a “direct in” at that terminal velocity. However, this seems to me to be a truly software-related problem. Yes, I know that setting various switches, is supposed to reset or kill a “loop” in the “code” however, in the good old days switches used to get connected to servo actuators by things called “wires” using stuff called “current”. Now each switch (however WW2 clunky) is read into a data set packet and sent along the Manchester bus data-highway of the revised and “simplified” cockpit systems into the various CPUs. Frantically pulling fuses out won’t help. So, ignoring the input side of the AoA sensors on the wings, there is a possibility that the software version now being hastily rolled out, (I’m not sure how the FCS/CPUS is updated, could even be over a USB stick) may indeed have the “corporate cover-up code” required to eliminate the “problem”. (i.e, if the loop executes say, more than 5 times, - it’s probably a sensor failure not a “pilot error”).
If any system which is designed to take a manual input before it re-enters its loops, does NOT read or ignores fresh inputs from switches - then there is also a risk that the “naughty” algorithm will continue to re-execute, despite the operators putting their big feet on the glass displays and yanking back with such enormous force as to bend the panel. In any event, there won’t be any real feedback or pitch reaction by the kite, if the control column is only “connected” to the air-surfaces by dumb electronics and computers. I doubt whether anyone has actually tried to see if the system does indeed go into an unrecoverable loop at FL 35 over the pond while delivering a new freshly painted bus to a punter. After these two incidents, I wouldn’t want to try, unless the hatch was open and I had a parachute - as I’m too fat to squeeze thru the DV window.
This brings me onto point 2).- “Sanity” Displays.
Each aircraft has 1-3 INS systems. They look at 6 DOF (six degrees of freedom, P,Y,R, and Surge Heave and Sway as Noah would say) and they are fully capable of measurements to high orders of angular and rate accuracy. They know exactly what the “vectorial” behaviour of the airframe is at any instant. The strapped down INS actually contains low-drift North-seeking Ring Laser gyroscopes, and 6 very sensitive accelerometers, probably all Honeywell types same as used in TLAAMs. The basic function of it can act as a really high-accuracy vertical reference unit. (remember those?). It can output the true measured “3D” motions of the a/c its - accelerations, pitch angles, rates and an earth-centred attitude reference. Remember - half the battle of flying is defying gravity. So as an engineer, my question is - why rely wholly on attitude sensors that Noah used to trim his boat in a gale? They are subject to bugs (insects), cleaners, de-icers, icing, birdstrikes, electronic failures, corrosion, static from lightning, poor calibration etc etc. The real method of display of an aircraft’s true attitude should, in my opinion, be derived from the “VRU” aspects of the INS and combined/checked against any external physical sensors. A failure warning “disagree” page should be available on the glass display, warning the pilot (by red/green overlaid lines etc) that what’s being “dealt with” is NOT the true attitude of the a/c in motion or its approach to/from instability. Just a thought. I’ve banned my whole family and staff from ever flying on the MAXes for the foreseeable future and I extend my heartfelt sympathies to those affected by this, IMHO, totally avoidable “modern” tragedy.